1. Field of the Invention
This invention relates to doctor blade systems, and is concerned in particular with an improved design that facilitates water or debris removal performance while maintaining desired doctor blade holder performance.
2. Description of the Prior Art
Many roll cleaning and sheet shedding applications on paper machines and other web handling applications involve doctor blade support devices commonly referred to as doctor blade holders. Typically, a doctor blade holder is mounted on a doctor-back, which is a heavy-duty beam that spans the paper machine width. The rear portion of a doctor blade is received into the holder, which supports the blade in a pre-determined position relative to a surface to be cleaned. The doctor blade holder works in concert with the doctoring assembly to apply the working edge of the blade, found on the blade's front portion, to an adjacent moving surface.
Certain conventional doctoring apparatus for paper machines are equipped with double doctors; the primary doctor cleans the surface of the roll, while the secondary blade carries away water and debris that may have dislodged from machined features such as holes and/or grooves in the roll surface, typically under affect of centrifugal force, with some additional influence from a reduction in fluid surface tension. This is, however, often not sufficient to adequately dewater the rolls.
U.S. Pat. No. 6,491,791 discloses a method and apparatus to clean roll surfaces or fabrics used in papermaking machines, wherein a doctoring element includes one or two integral doctor blades as well as an integral gas chamber that provides pressurized gas, e.g., compressed air, to the outgoing side of a doctoring apparatus having one doctor blade, and to the inter-blade area of a doctoring apparatus having two doctor blades. The compressed air is provided to enhance the water or dirt removal capabilities. Each of the disclosed apparatus involves doctor blades that are integral with the structure forming the gas chamber within the doctoring element. The apparatus including a two blade doctoring element, for example, provides that the interblade space forms a closely and tightly delineated pocket into which compressed air may be passed ('791 patent, col. 3, lines 18-20). The high pressure compressed air is disclosed to escape under the doctor blades via grooves on the grooved-shell roll being processed ('791 patent, col. 6, lines 59-63).
The use of such integral doctor blades requires that the entire doctoring element be replaced whenever the doctor blades become too worn. The doctoring apparatus are also not disclosed to be position adjustable with respect to the roll, and it is not at all clear how such an integral gas chamber may be incorporated in a doctoring apparatus that provides adjustable position accuracy with respect to a roll as well as flexibility in doctoring a roll along an elongated length of the doctor blade. Further shortcomings of such systems include: 1) The apparatus is not integral with the holder. 2) The apparatus is part of the blade and thus when it is worn or damaged it must be replaced, which is very costly. 3) The apparatus is very rigid and lacks the ability to conform well to the roll surface. 4) The air discharge features and geometry used for the purpose of dewatering can fail to produce adequate dewatering. 5) The apparatus air discharge is always open allowing contaminants to enter from the ambient when the device is not pressurized; the ingress of contaminants may be avoided by applying pressurized air when the machine is under maintenance, but with the disadvantage of the added cost associated with it.
U.S. Pat. No. 6,139,638 discloses a doctor blade holder apparatus that includes a planar upper holding member that is pivotally mounted to a tray such that the position of the upper holding member with respect to the tray may be adjusted by unloading and loading tubes. The upper holding member also includes a plurality of distribution passages that are coupled respectively off of the upper holding member via a plurality of branch conduits to a common header. The pressurized fluid, therefore, must separately travel through the conduits to reach each of the individual areas along the doctor blade holder apparatus, while maintaining sufficiently equalized pressure as the fluid is directed toward the roll along the elongated length of the doctor blade.
There remains a need, therefore, for a cost effective doctor blade holder system that facilitates consistent debris removal without limiting the flexibility of the doctor blade holder system or the effectiveness of the doctoring process, and in particular that improves the dewatering performance of a doctor apparatus operating on various paper machine rolls, while retaining or improving the cleaning performance of the doctor blade, such as, for example in a machine for doctoring a paper machine suction press.